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Electromagnetic Induction

Electromagnetic Induction. I can cause B. Can B cause I?. YES!. We need:. Loop (complete circuit). Magnetic Field. THE EMF INDUCED IN A MOVING CONDUCTOR. Each charge within the conductor is moving and experiences a magnetic force . The separated charges on the

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Electromagnetic Induction

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  1. Electromagnetic Induction

  2. I can cause B Can B cause I? YES! We need: Loop (complete circuit) Magnetic Field

  3. THE EMF INDUCED IN A MOVING CONDUCTOR Each charge within the conductor is moving and experiences a magnetic force The separated charges on the ends of the conductor give rise to an induced emf, called a motional emf.

  4. Motional emf when v, B, and L are mutually perpendicular

  5. Example 1 Operating a Light Bulb with Motional Emf Suppose the rod is moving with a speed of 5.0m/s perpendicular to a 0.80-T magnetic field. The rod has a length of 1.6 m and a negligible electrical resistance. The rails also have a negligible electrical resistance. The light bulb has a resistance of 96 ohms. Find (a) the emf produced by the rod and (b) the current induced in the circuit.

  6. MOTIONAL EMF AND ELECTRICAL ENERGY In order to keep the rod moving at constant velocity, the force the hand exerts on the rod must balance the magnetic force on the current:

  7. Conceptual Example 3 Conservation of Energy A conducting rod is free to slide down between two vertical copper tracks. There is no kinetic friction between the rod and the tracks. Because the only force on the rod is its weight, it falls with an acceleration equal to the acceleration of gravity. Suppose that a resistance connected between the tops of the tracks. (a) Does the rod now fall with the acceleration of gravity? (b) How does the principle of conservation of energy apply?

  8. MOTIONAL EMF AND MAGNETIC FLUX magnetic flux

  9. I can cause B B can cause I There are 3 ways to induce I: 1) Change B 3) Change the orientation of the loop 2) Change the area of the

  10. All these changes cause ΔΦ ΔΦ – magnetic flux

  11. Example 1 • Wire is 16cm long • B1 =4.0mT • Find magnetic flux if: • A) it’s a square • B)it’s a rectangle with one side = 2.0m

  12. Example 1 • Wire is 16cm long • B1 =4.0mT • Find magnetic flux if: • A) the square is perpendicular to the field • B)the square makes a 60o angle with the field

  13. LENZ’S LAW • The induced emf resulting from a changing magnetic flux has a polarity that leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change. • BLAH – BLAH – BLAH … • Change of B creates current Current will have its own B around it • INDUCED B always FIGHTS THE CHANGE: • If the flux is growing, it will fight it ( ) • If the flux is dying, it will help it ( )

  14. There is a constant magnetic field directed into the page in the shaded region. The field is zero outside the shaded region. A copper ring slides through the region. For each of the five positions, determine whether an induced current exists and, if so, find its direction.

  15. How strong is I induced? What does current depend on? (Remember this guy  Where would V come from if there is no battery? Just the wire…. No battery = no ‘terminal voltage’ – only emf

  16. FARADAY’S LAW OF ELECTROMAGNETIC INDUCTION The average emf induced in a single coil is

  17. The Emf Induced by a Changing Magnetic Field A coil of wire has an area of 0.0015 m2. A magnetic field is perpendicular to the surface. Initially, the magnitude of the magnetic field is 0.050 T and 0.10s later, it has increased to 0.060 T. Find the average emf induced in the coil during this time. What would be the total emf if we had 20 coils?

  18. FARADAY’S LAW OF ELECTROMAGNETIC INDUCTION The average emf induced in coil with N loops is

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